This invention relates to a process for halogenating with Cl.sub.2 or Br.sub.2 telomers of tetrafluoroethylene characterized in that they have, at one end of their chain, a iodine end group, the other end group being selected from chlorine, bromine or iodine, and in which the products obtained consist of C.sub.2 F.sub.4 units repeated n times, in which n varies from 2 to 6, extremes included, and the end groups of the chain are equal or different from each other and are selected from chlorine or bromine.
Known in the art and industrially produced are haloperfluoroalkanes, which are utilized in many technological fields depending on their chemical and chemical-physical characteristics.
A limitation to the use thereof is caused by their low boiling point, as is apparent from the following Table.
______________________________________ Boiling point Chemical formula (.degree.C. at 1 at. abs.) Examples of fields of use ______________________________________ CCl.sub.3 F +23.8 Aerosol, foaming of poly= urethanes CCl.sub.2 F.sub.2 -29.8 Aerosol, refrigeration, foaming of polyolefins CHClF.sub.2 -40.8 Refrigeration C.sub.2 Cl.sub.3 F.sub.3 +47.6 Solvent, foaming of resins C.sub.2 Cl.sub.2 F.sub.4 +3.6 Aerosol, foaming of poly= olefins C.sub.2 ClF.sub.5 -39.1 Refrigeration CBrF.sub.3 -57.8 Flame extinguishing agent C.sub.2 Br.sub.2 F.sub.4 +46.7 Flame extinguishing agent ______________________________________
These products, therefore, are utilizable only in fields where no high boiling points are required.
The synthesis methods known so far for preparing products exhibiting a higher molecular weight and by consequence a higher boiling point, having general formula Cl(C.sub.2 F.sub.4).sub.n Cl with n .gtoreq.2, are little selective or unsuited for a commercial-scale utilization.
For example in U.S. Pat. No. 3,381,043 it is stated that the addition reaction of chlorine to C.sub.2 F.sub.4 is too strong as to be capable of giving rise to telomerization. In practice that means that the reaction stops at the first group ClC.sub.2 F.sub.4 Cl and does not permit to introduce further units C.sub.2 F.sub.4 between the two chlorine atoms in order to obtain the higher homologous products.
The above cited patent describes a process for preparing by telomerization the groups higher than ClC.sub.2 F.sub.4 Cl by operating in the presence of PCl.sub.5. However, the reaction with PCl.sub.5, owing to the fact that this product is solid, requires the presence of solvents to promote a higher contact between the reagents. Generally, CCl.sub.4 is used as a solvent.
In this case, however, the degree of utilization of the systems employed for the synthesis results to be reduced, with consequent considerable increase in the production costs.
Furthermore, according to said patent, the obtained products can be separated only by using gaschromatographic techniques. In fact, a fractioned distillation appears impossible for products Cl(C.sub.2 F.sub.4).sub.n Cl wherein n.ltoreq.4 because of the formation of azeotropes between Cl(C.sub.2 F.sub.4).sub.3 Cl and CCl.sub.4 employed as a solvent.
Only the fractions having n&gt;4 can be obtained by means of the distillation technique.
However, the products with n.ltoreq.4 are the most interesting from a practical viewpoint.
This process for the preparation of telomers is of no practical interest from an industrial aspect because it is not proposable to use gaschromatographic techniques for preparing considerable amounts of the individual telomers with n.ltoreq.4.